Official reviews into deaths or serious injuries of abused and neglected children are still consistently finding the professionals charged with protecting them failing to do their jobs properly, according to a watchdog's report published today.

Ofsted also judged that fewer than half of the serious case reviews (SCRs) it examined were better than adequate and 16% were inadequate for the year up to March. The 147 reviews, which covered 194 children, 90 of whom died and 119 were known to social services, showed that authorities were frequently too trusting of parents in families where abuse was possible.

This week a SCR into the death of Peter Connelly, published in full for the first time, was highly critical of agencies in Haringey, north London, for continuously accepting his mother's accounts of how he had come to be injured. She, her boyfriend and his brother were later jailed for causing or allowing the 17-month-old's death.

Ofsted's report said: "Parents' explanations for bruising and other injuries were too readily accepted … without further examination of the child or consultation with named child protection doctors or nurses ... Similarly, social care staff often found it difficult to identify chronic neglect because of parents' feigned compliance with social work interventions."

Some 42% of the SCRs were found to be of a good standard, with the same proportion rated as adequate. Four of the SCRs were in Haringey, with three rated good and one adequate. None were outstanding, though the figures are an improvement on last year when 23% were good and 34% inadequate. The majority of the children were five or younger and a quarter were subject to a child protection plan.

Problems arose not owing to a lack of systems and guidelines but staff failure to adhere to them. Information was not shared between agencies like police and social services properly, while too often the focus on the child was lost.

Crucial steps were not taken because of gaps in services, children's needs being considered enough, "professional drift" and workers simply making the wrong decisions.

GPs, often the first point of contacts for families, were sometimes unclear when they should refer cases to social services. In some cases local authorities' legal services failed to use powers available to protect children by taking them into care.

Children voices were not always heard. A 12-year-old girl whose mother had a long history of drug abuse and was known to social services who suffered a serious sexual attack by an man known to her mother had only been talked to once. But even though her views "shouted out so clearly" from that occasion, she was left in circumstances where she was vulnerable.

The report also found that many reviews are not being completed quickly enough, with only 60 completed in the set six-month timescale. Another 19 took between one and two years and eight took over two years.

Ofsted concluded: "It is still of concern that inspectors found 23 reviews evaluated during this period to be inadequate."